Photoconductive compositions and imaging members and methods employing same

ABSTRACT

Photoconductive composition comprising a carbazole functional polymer wherein at least 0.1 percent of said carbazole function groups have the following structural formula ##SPC1## 
     wherein X is a structural unit of said polymer; R is hydrogen; an aliphatic hydrocarbon radical having from 1 - 10 carbon atoms; phenyl; or substituted phenyl, said phenyl substituents being capable of contribution of electrons to relatively electron deficient centers with the structural unit. 
     Materials of the above structural formula can be readily polymerized or copolymerized with other addition polymers. These polymer compositions are useful in preparation of photoconductive insulating layers for electrophotography.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser. No. 374,157 filed June 27, 1973, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to organic polymeric photoconductive compositions and the use of such compositions in electrophotographic imaging members and methods. More specifically, this invention concerns itself with inherently photoconductive compositions which are characterized by their high extinction coefficients and good spectral response at wavelengths of from about 4,200 - 6,200 A.

2. Description of the Prior Art

The formation and development of images on the imaging surfaces of photoconductive materials by electrostatic means is well-known. The best known of the commercial processes, more commonly known as xerography, involves forming a latent electrostatic image on the imaging surface of an imaging member by first uniformly electrostatically charging the surface of the imaging layer in the dark and then exposing this electrostatically charged surface to a light and shadow image. The light struck areas of the imaging layer are thus rendered conductive and the electrosttic charge selectively dissipated in these irradiated areas. After the photoconductor is exposed, the latent electrostatic image on this image bearing surface is rendered visible by development with a finely divided colored electroscopic material, known in the art as "toner". This toner will be principally attracted to those areas on the image bearing surface which retain the electrostatic charge and thus form a visible powder image.

The developed image can then be read or permanently affixed to the photoconductor where the imaging layer is not to be reused. This latter practice is usually followed with respect to the binder-type photoconductive films (e.g. ZnO) where the photoconductive imaging layer is also an integral part of the finished copy.

In so-called "plain paper" copying systems, the latent image can be developed on the imaging surface of a resuable photoconductor or transferred to another surface, such as a sheet of paper, and thereafter developed. When the latent image is developed on the imaging surface of a reusable photoconductor, it is subsequently transferred to another substrate and then permanently affixed thereto. Any one of a variety of well-known techniques can be used to permanently affix the toner image to the copy sheet, including overcoating with transparent films, and solvent or thermal fusion of the toner particles to the supportive substrate.

In the above "plain paper" copying system, the materials used in the photoconductive layer should preferably be capable of rapid switching from insulating to conductive to insulating state in order to permit cyclic use of the imaging surface. The failure of a material to return to its relatively insulating state prior to the succeeding charging sequence will result in a decrease in the maximum charge acceptance of the photoconductor. This phenomenon, commonly referred to in the art as "fatigue", has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity. Typical of the materials suitable for use in such a rapidly cycling system include anthracene, sulfur, selenium and mixtures thereof (U.S. Pat. No. 2,297,691); selenium being preferred because of its superior photosensitivity.

In addition to anthracene, other organic photoconductive materials, most notably, poly(N-vinylcarbazole), have been the focus of increasing interest in electrophotographic, U.S. Pat. No. 3,037,861. Until recently, neither of these organic materials have received serious consideration as an alternative to such inorganic photoconductors as selenium, due to fabrication difficulties and/or to their relative lack of speed and photo-sensitivity. The recent discovery that high loadings of 2,4,7-trinitro-9-fluorenone in polyvinylcarbazoles dramatically improves the photoresponsiveness of these polymers has led to a resurgence in interest in organic photoconductive materials, U.S. Pat. No. 3,484,237. Unfortunately, the inclusion of high loadings of such activators can and usually does result in phase separation of the various materials within such compositions. Thus, there will occur within these compositions regions having an excess of activator, regions deficient in activator and regions having the proper stoichiometric relationship of activator to photoconductor. The maximum amount of activator that may be added to most polymeric photoconductive materials without occasioning such phase separation generally will not exceed in excess of about 6 - 8 weight percent.

One method suggested for avoiding the problems inherent in the use of such activators in conjunction with polymeric photoconductors, is the direct incorporation of the activators into the polymeric backbone of the photoconductor, U.S. Pat. No. 3,418,116. In this patent is disclosed the copolymerization of a vinyl monomer having an aromatic and/or heterocyclic substituent capable of an electron donor function with a vinyl monomer having an aromatic and/or heterocyclic substituent capable of an electronic acceptor function. The spatial constraint placed upon these centers of differing electron density favors their charge transfer interaction upon the photoexcitation of such a composition. These so-called "intramolecular" charge transfer complexes, more accurately designated "intrachain" charge transfer complexes, are believed to function substantially the same as charge transfer complexes formed between small activator molecules and a photoconductive polymer. The fact that the electron donor function and an electron acceptor function are on a common polymeric backbone does not apparently change the π - π charge transfer interaction, but merely increases the probability of it occurring. Unfortunately, the preparation of such copolymers from vinyl monomers having electron donor center and vinyl monomers having an electron acceptor center is often beset with difficulty.

Accordingly, it is the object of this invention to provide a polymeric photoconductive composition which is highly photosensitive and yet relatively easy to prepare.

More specifically, it is the object of this invention to provide a polymeric photoconductive composition capable of an intramolecular charge transfer transition.

It is another object of this invention to provide a polymeric photoconductive composition wherein an electron donor and an electron acceptor center are contained within a single structural unit of the polymer.

It is yet another of the objects of this invention to provide a polymeric photoconductive composition having good spectral response to light in the visible region of the electromagnetic spectrum.

SUMMARY OF THE INVENTION

The above and related objects are accomplished by providing a photoconductive composition comprising a carbazole functional polymer wherein at least 0.1 percent of said carbazole functional groups have the following structural formula ##SPC2##

wherein X is a structural unit of said polymer R is hydrogen; an aliphatic hydrocarbon radical having anywhere from 1 - 10 carbon atoms; phenyl; or substituted phenyl, said phenyl substituents being capable of contribution of electrons to relatively electron deficient centers with the structural unit.

With the electron donor and electron acceptor centers being located within a single structural unit of the polymer the electronic transition moment and flow of charge upon photoexcitation are colinear and thus intramolecular charge transfer occurs within this structural unit. The photoresponse of this composition is therefore highly efficient since it is both independent of the relative concentration of electron donor and electron acceptor centers within the composition and substantially independent of a π - π type charge transfer interaction.

In the preferred embodiments of this invention, (a) at least 35 to about 50% of the carbazole functional groups of the carbazole functional polymer have the hereinbefore described structural formula and (b) the polymeric composition comprises structural units having the hereinbefore described structural formula and structural units from N-ethyl-3-vinylcarbazole.

DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS

Polymeric photoconductive compositions containing structural units of the type hereinbefore described can be readily prepared from carbazole functional polymers by tricyanovinylation of said carbazole functional groups with tetracyanoethylene under the appropriate process conditions. The starting materials used in this synthesis can be almost virtually any 2 or 3 carbazyl functional polymer provided that the backbone of said polymer does not have other functional groups which are capable of interference with the tricyanovinylation of these carbazole groups or which would substantially adversely effect the charge storage characteristics and/or photoresponsiveness of the desired photoconductive composition.

Among the polymers which can be used in the synthesis of the photoconductive compositions of this invention include poly (3-vinylcarbazole); poly(2-vinylcarbazole); poly(3-vinyl-N-ethyl carbazole); poly(2-vinyl-N-ethyl carbazole); poly(3-vinyl-N-phenyl carbazole); poly(2-vinyl-N-phenyl carbazole); poly(3-vinyl-N-(p-dimethylamino-phenyl)-carbazole); poly(2-vinyl-N-(p-dimethylaminophenyl)-carbazole); poly(methyl-(3-carbazyl) siloxane); poly(methyl(N-ethyl-3-carbazyl) siloxane); poly(methyl-N-ethyl-2-carbzyl) siloxane); poly(methyl-(N-phenyl-3-carbazyl) siloxane); poly(methyl(N-phenyl-2-carbazyl) siloxane); poly(methyl-(N(p-dimethylaminophenyl)-3-carbazyl) siloxane); poly(methyl-(N(p-dimethylamine-phenyl) 2-carbazyl)siloxane); poly(3-carbazyl-acrylamide) and copolymers thereof. The backbone of carbazole functional polymers used in this synthesis can also contain non-carbazole containing structural units. With regard to the carbazole functional addition polymers, such non-carbazole functional structual units can be contributed by such monomers as acrylic acid; methacrylic acid; methylmethacrylate; butymethacrylate; styrene; isoprene; and copolymers thereof. With regard to the carbazole functional siloxane polymers, such noncarbazole structural units can be contribued by materials such as dialkyl siloxy units.

Tricyanovinylation of these carbazole functional polymers can be effected by combining one or more of such polymers and tetracyanoethylene in a solvent, such as dimethylformamide, under the appropriate conditions. Good results are obtained when the relative concentration of tetracyanoethylene is equal to about 0.5 to about three times the mole equivalent of pendant carbazole groups of the carbazole functional polymer. The equation which follows is illustrative of tricyanovinylation of poly(N-ethyl-3-vinylcarbazole). ##SPC3##

wherein n is the number of N-ethyl-3-vinylcarbazole units of the polymer and m is about 0.1 to about 50 mole percent.

The tricyanovinylated polymer thus prepared is a solid polymeric material having an average molecular weight preferably in excess of about 15,000.

The carbazole functional polymers used in the above and similar synthesis are generally not readily commercially available; however, they can be readily prepared by techniques and with equipment disclosed in the technical literature.

In the above synthesis, it is generally preferred that the carbazole functional polymer and the tetracyanoethylene be prepared in separate dimethylformamide solutions; the polymeric material being dissolved in the reaction vessel. The reaction vessel should be provided with a magnetic stirring bar, a reflux condenser and an addition funnel; the tetracyanoethylene solution being prepared in the addition funnel. Once the above principal reactants are in solution, the reaction vessel containing the carbazole functional polymer is purged with nitrogen and the temperature of the reaction vessel gradually increased. After the temperature of the polymer solution reaches the desired level (generally in the range of about 60° to about 140°C), the tetracyanoethylene solution is added to the polymer solution in predetermined amounts over the prescribed reaction interval. As the polymer and tetracyanoethylene interact, a highly colored metastable intermediate is formed which upon further heating ultimately dissociates thus yielding the desired product. In the event of abrupt addition of relatively large concentrations of tetracyanoethylene to the polymer, extensive complexing of the two materials will result, causing gelation and/or precipitation of the polymeric reactant. This is minimized by the gradual addition of tetracyanoethylene solution to the reaction vessel over a period which can range anywhere from a few hours to several days, depending upon the degree of substitution desired. The degree of tricyanovinylation of the carbazole functional polymer, is generally believed to be limited only by the number of pendant carbazole groups available for tricyanovinylation. It is not unusual to have anywhere from about 35 to about 50% of the pendant carbazole groups present modified under the conditions outlined above.

Factors such as time, temperature and rate of addition of the tetracyanoethylene solution to the reaction vessel can effect the degree of modification of the polymer as well as the physical properties of the product obtained. Under certain conditions, even the solvent within which the above reactants are combined can effect the relative rate of formation of the desired product. For example, when the carbazole functional polymer and tetracyanoethylene are combined in a solvent, such as tetrahydrofuran or trichloroethane, the intermediate formed during the interaction of the polymer and the tetracyanoethylene is relatively stable and thus the desired reaction product forms somewhat more reluctantly. In contrast to the above, when the same reactants are combined in the solvent, dimethylformamide, the intermediate formed readily dissociates to the desired product.

Reaction of the polymer and the tetracyanoethylene can be carried out at temperatures in the range of from about 60° to about 140°C. In the event that an increase in the rate of reaction is desired, the contents of the vessel can be pressurized and thus the boiling point of the solvent elevated, allowing the reaction to proceed at a somewhat accelerated pace.

In order to insure uniform mixing of the polymer and the tetracyanoethylene solutions, the contents of the reaction vessel are maintained in a constant state of mild agitation.

As indicated previously, it is generally preferred that the reaction vessel be purged of air prior to the addition of the tetracyanoethylene solution to the polymer solution. This can be readily achieved by purging the reaction vessel with an inert gas, such as nitrogen.

Upon completion of the addition of tetracyanoethylene to the reaction vessel and its interaction with the polymer to the extent desired, agitation of the reaction mass ceases and the contents of the vessel are allowed to cool to room temperature. The relative viscosity of the polymeric materials contained within the vessel appears somewhat greater than initially observed and little if any gelation of the polymer has occurred. In the event that some precipitate is present within the reaction vessel, it is removed by filtration. The polymeric composition is then separated from the reaction medium by precipitation with a lower alkyl alcohol, such as methanol, the polymer solids collected by filtration and residual solvent removed therefrom under a vacuum. The polymer can then be further purified by repeated dissolution and reprecipation.

The polymeric composition thus prepared can be formed into substantially uniform coherent and adherent films on any suitable substrate by standard coating and film forming techniques. After applying a coating of such material to a substrate, the resultant film is allowed to dry until substantially free of residual solvent.

The vehicle used in the dissolving of this polymeric material in preparation of such films can be toluene, cyclohexanone, tetrahydrofuran, as well as other suitable inert organic solvents or solvent mixtures. The quantity of this polymer solution which can be applied to such substrates need be carefully monitored to insure that the resulting deposit is coherent and forms a substantially uniform film on the supportive member. Generally, film thickness is controlled in a dip coating type application by adjustment of the viscosity of this solution and/or by control of the temperature and humidity of the post coating environment. In the event that the polymeric layer is prepared by solvent casting of the polymer solution on a supportive member, mechanical means can also be used in addition to adjustment in viscosity to control the film thickness of the photoconductive film. For example, the use of a doctor blade having a wet gap setting of about 0.005 inches to assist in spreading the dispersion over such a substrate will insure that the film thickness of the imaging layer will not exceed about 15 microns. Photoconductive films prepared from these polymeric compositions having thicknesses in the range of from about 1 to about 50 microns are useful in electrophotographic imaging members.

Virtually any of the traditionally employed conductive self supporting substrates used in the preparation of electrophotographic imaging members can be operatively associated with the photoconductive films prepared as described above. Typical of the materials which can be satisfactorily used in preparation of such imaging members include aluminum; chromium; stainless steel; brass; copper; beryllium copper; their respective alloys; polyethyleneterephthalate (Mylar) coated with a thin aluminum film; and a glass substrate having a thin coating of tin oxide.

The photoconductivity of such films is evaluated by standard xerographic discharge techniques (a) using continuous white light; (b) using a pulsed light; (c) and in a sandwich cell type configuration using continuous monochromatic radiation. As a result of such evaluation, it appears that the films of these photoconductive compositions exhibit good spectral response at wavelengths in the range of from about 4200 to about 6200 A and have a photoresponsiveness comparable to commercially available poly(N-vinylcarbazole) photoconductors.

Photoconductive imaging members prepared as described above can be used in electrophotography, and, more specifically are suitable in electrostatographic imaging. In a typical electrostatographic process, the surface of the photoconductive imaging layer is sensitized with a corona electrode by the application of a substantially uniform electrostatic charge to said surface. This charge can then be selectively dissipated by illumination of the charged surface in imagewise configuration with activating electromagnetic radiation, thus forming a latent electrostatic image on the imaging surface. The resulting latent image is rendered visible by development with electroscopic toner materials having a polarity opposite to that of the latent image. The development of said image can be performed eiter directly on the photoconductive layer or the latent image transferred to a receiving sheet where it is thereafter developed.

In certain operational environments, it may be advantageous for such an imaging member to be provided with an interfacial barrier layer disposed intermediate between the imaging layer and the conductive substrate. This type of barrier is intended to provide a blocking contact so as to prevent premature injection of charge carriers from the conductive substrate into the photoconductive imaging layer, and thus improve its charge storage capacity. A second technique used in improving the charge storage capability of such an imaging member is to provide said member with an insulating overcoating. Such insulating overcoating should be of a thickness sufficient to support the surface charge without undergoing dielectric breakdown. Generally the resistivity of such an overcoating and the barrier layer should be in excess of about 10¹⁰ ohm-centimeters.

The Examples which follow further define, describe and illustrate preparation, use and evaluation of the photoconductive compositions of this invention. The apparatus, process, conditions and techniques used in such preparation and evaluation are presumed to be standard or as hereinbefore described. Parts and percentages appearing in these Examples are by weight unless otherwise specified.

EXAMPLE I Preparation of tricyanovinylated poly(N-ethyl-3-vinylcarbazole)

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly (N-ethyl-3-vinylcarbazole). The monomer of this polymer is synthesized from N-ethyl-carbazole-3-carboxaldehyde in accord with the procedures described by G. Wittig et al for preparation of olefins from alkylidenephosphoranes and carbonyl compounds -- the so-called Wittig synthesis -- Chem. Ber. 87, 1318 (1954) and Chem. Ber., 88, 1655 (1955). N-ethyl-3-vinylcarbazole is prepared as follows: triphenylmethylphosphonium bromide, 35.72g (0.1 mole), and 300 ml anhydrous tetrahydrofuran (THF) are placed in a 2 liter three necked flask. The contents of the flask is blanketed with argon and then 46 ml of a 2.18 molar solution of butyllithium in hexane (0.1 mole) is added to the vigorously stirred solution over a period of 15 minutes. The reaction mixture is allowed to react for 2 hours and then N-ethylcarbazole-3-carboxaldehyde, 22,33g (0.1 mole) in 150 ml THF added to the reaction flask over a period of 10 minutes. After heating to boiling under reflux conditions for 1.5 hours the reaction mixture is cooled to room temperature and treated with 750 ml hexane. After the precipitate which forms is discarded, the solvents are removed thus yielding a crude product which crystallizes on standing. Recrystallization is accomplished with a minimum amount of ethanol containing a drop of ammonium hydroxide. Yield 11.5 g (52%) of N-ethyl-3-vinylcarbazole M.P. 66° - 67°C.

The N-ethyl-3-vinylcarbazole is then purified on a silica gel column and eluted with hexane. Prior to dissolving this monomer, the polymerization solvent, spectrograde methylene chloride, is passed through a neutral alumina column and then used immediately. N-ethyl-3-vinyl-carbazole, 4.0g, in 80 ml of methylene chloride is placed in a 100 ml 2-necked flask and blanketed with dry nigrogen. The solution is cooled to -60°C and then 8 microliters of boron trifluoride (etherate in 2 ml methylene chloride) is added to the monomer solution which is being rapidly stirred with a magnetic stirring bar. After a few minutes, the viscosity of the solution increases to a point at which further stirring becomes difficult. The reaction mixture is then quickly quenched in 400 ml methanol. The THF soluble polymer is reprecipitated several times with methanol. Yield 2.8g, Mn330,000, MWD 2.97.

A solution comprising 20 grams of poly(N-ethyl-3-vinylcarbazole)-- average molecular weight 330,000 and molecular weight distribution 2.97 -- in 400 milliliters dimethylformamide (DMF) is placed in 3 neck 1 liter round bottom flask equipped with a nitrogen inlet, a magnetic stirring bar, a thermometer, a reflux condenser and an addition funnel. A second solution comprising 38.5 grams tetracyanoethylene in 150 milliters DMF is prepared and placed in the addition funnel. The flask containing the polymer solution is purged of air with nitrogen, heated to and maintained at about 60°C under nitrogen and the tetracyanoethylene solution added in equal increments over a 4 day period. The contents of the flask are maintained under a blanket of nitrogen at the above temperature and in a constant state of mild agitation during the 4 day interval. At the end of the 4 day period, heating ceases and the contents of the flask are allowed to cool to room temperature (˜ 20°C). Any DMF insoluble material is separated and the DMF soluble and the polymer recovered by precipitation with methanol followed by filtration. Residual DMF is removed from the recovered polymer solids by drying overnight in a vacuum oven at 25°C. The dried polymer solids are then repeatedly reprecipitated from water and methanol in a Waring Blender for removal of colored impurities.

Analytical results of such synthesis are as follows:

Yield: 19 grams

Average Mol. Wt.: 310,000 (as determined by gel permeation chromatography)

Molecular Wt. Distribution: 2.97

λ_(max) ^(THF) 503 nm (1.4 × 10⁴)

Degree of tricyanovinylation 28% (based upon No. of N-ethyl-carbazole functional groups)

The polymeric composition prepared as described above is then dissolved in a series toluene/cyclohexanone (4:1) solutions and cast on scrubbed aluminum plates. The relative concentration of polymeric composition in the casting solvent is varied so as to enable preparation of photoconductive films of differing thickness. These films are allowed to dry overnight at room temperature and then placed in a vacuum chamber at 110°C for one hour for further removal of residual solvent. The photoconductive films thus prepared have a dry film thickness in the range of from about 5 to about 25 microns.

These films are then evaluated for spectral sensitivity and their rate of photodischarge determined by traditional xerographic techniques. The spectral response of such films are in the range of from about 4200 to 6200 A with a peak sensitivity at about 4960 A. The rate of photoinduced discharge of a positive and a negative surface potential of this composition is comparable to commercial poly(N-vinylcarbazole) photoconductors, (available from IBM Corporation, Armonk, N. Y.).

EXAMPLE II

Attempts were also made to prepare photoconductive films from poly(N-ethyl-3-vinylcarbazole) having loadings of tetracyanoethylene equivalent to the degree of tricyanovinylation of the more highly photoresponsive compositions of this invention. It was discovered that it was not technically feasible to incorporate substantially in excess of about 5 to about 10% by weight of tetracyanoethylene in poly(N-ethyl-3-vinylcarbazole) due to problems associated with phase separation and crystallization of this activator within the polymer matrix. Even at these relatively low concentrations, the resulting films are chemically unstable and, therefore, the electronic properties undergo what appears to be a continual shift. Moreover, films containing even these low loadings of tetracyanoethylene are mechanically inferior to the films prepared from the compositions of this invention.

EXAMPLE III

An imaging member having a photoconductive insulating layer of the compositions of the films of Example I is charged to a positive potential of about 600 volts in the dark, exposed to a light and shadow image whereby the surface charge is selectively dissipated in the light struck areas thus forming a latent image. The latent image is then rendered visible by development with colored electroscopic toner particles and the toner image transferred to a receiving sheet. The toner image is permanently affixed to said receiving sheet by thermal fusion. The imaging member is then cleaned of residual toner, the charge pattern remaining on its surface (if any) neutralized by a corona of an opposite polarity and the imaging sequence repeated once again. The reproductions prepared by the above method are evaluated visually and are deemed to be of acceptable quality.

EXAMPLE IV - VI

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(N-ethyl-2-vinylcarbazole). This polymer can be synthesized in accord with the procedures described by Hyde, Kricke and Ledwith in Polymers 14, 124 (1973). According to their method, a mixture of 24 grams 2-acetyl carbazole and 40 gram aluminum isopropoxide in 75 milliliters of xylene is heated to boiling under reflux conditions and such heating continued for three hours, during which time acetone forms within the mixture and is removed therefrom by distillation. Upon cooling, particulates (principally aluminum isopropoxide) are removed from the mixture by filtration and the filtrate collected in water. Upon standing the xylene and aqueous layers separate whereupon the xylene is drawn off and the aqueous layer subsequently extracted with three 60 milliliter portions of ether. The combined extracts are washed with water and dried over anhydrous magnesium sulfate (MgSO₄ /NaOH). Evaporation of the ether yields 2-vinylcarbazole. This monomer can be alkylated by simply contacting a solution of said monomer in dimethylformamide/ether with thallous ethoxide/alkyl iodide (excess). The monomer thus prepared can be readily formed into polymers by standard free radical, cationic and/or anionic polymerization techniques.

    ______________________________________                                         Example No. Carbazole Functional Polymer                                       ______________________________________                                         IV          poly(2-vinylcarbazole)                                             V           poly(N-ethyl-2-vinylcarbazole)                                     VI          poly(N-methyl-2-vinylcarbazole)                                    ______________________________________                                    

The polymeric products thus attained are reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in each synthesis is three times the mole equivalent of the carbazole functional groups present on each polymer.

EXAMPLE VII

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(3-vinylcarbazole). The monomer from which this polymer is formed can be prepared by techniques analogous to those described for preparation of the monomer of Example IV. Polymerization of this monomer and its subsequent tricyanovinylation also parallel the procedures of Example IV.

EXAMPLE VIII

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(N-phenyl-3-vinylcarbazole). This polymer can be prepared by techniques analogous to those employed in Example I.

The polymer product thus attained is reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in such synthesis is three times the mole equivalent of the carbazole functional groups present on this polymer.

EXAMPLE IX

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(N-(p-dimethylamino-phenyl)-3-vinylcarbazole). This polymer can be prepared by techniques analogous to those used in Example I.

The polymer product thus attained is reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in such synthesis is three times the mole equivalent of the carbazole functional groups present of this polymer.

EXAMPLE X

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(N-phenyl-2-vinylcarbazole). This polymer can be prepared by techniques analogous to those employed in Examples IV - VI.

The polymer product thus attained is reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in such synthesis is three times the mole equivalent of the carbazole functional groups present on this polymer.

EXAMPLE XI

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(N-p-dimethylamino-phenyl)-2-vinylcarbazole). This polymer can be prepared by techniques analogous to those used in Example IV - VI.

The polymer product thus attained is reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in such synthesis is three times the mole equivalent of the carbazole functional groups present on this polymer.

EXAMPLE XII

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(3-carbazyl-acrylamide). This polymer can be prepared by a synthesis analogous to that described in U.S. Pat. No. 3,307,940 (Example Ic) which is hereby incorporated by reference. The monomer of this polymer is prepared as follows: a solution of 3-amino-carbazole in dioxane is chilled to about 0°C and stoichiometric quantities of acrylic acid chloride added thereto dropwise while the solution is continuous agitated. Upon completion of addition acrylic acid chloride, stirring of the solution is continued for an additional 15 minutes during which time a reaction product separates out. This solution is now made alkaline by the addition thereto of sodium bicarbonate, allowed to stand at room temperature overnight, and the reaction product, 3-carbazyl-acrylamide crystallized from methanol (melting point 21° - 211°C). The monomer thus attained can be formed into polymers by standard polymerization techniques.

This polymeric product is reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in such synthesis is three times the mole equivalent of the carbazole functional groups present on this polymer.

EXAMPLE XIII

The carbazole functional polymer which is tricyanovinylated according to the procedures specified hereinafter is poly(methyl-(N-ethyl-3-carbazyl) siloxane. This polymer can be prepared by acid catalyzed hydrolysis of methyl-(N-ethyl-3-carbazyl) dimethoxysilane in accord with the procedures described in the technical literature (e.g. W. Noll, Chemistry and Technology of Silicone, Academic Press, New York (1968) p.p. 197 - 199; and K. A. Andriannov, Metallo Organic Polymers, Intersciences Publishers, New York, p.p. 121-123. In accord with their teachings, methyl-(N-ethyl-3-carbazyl) dimethyoxysilane is placed in a reaction vessel and a small quantity of water and hydrochloric acid added thereto. The resulting solution is gently heated to about 60°C for a period sufficient to hydrolyze substantially all methoxy groups from the silane. The concentration of water is critical and must be carefully controlled so as to favor the formation of linear siloxane polymers from these materials. The products thus isolated is poly(methyl(N-ethyl-3-carbazyl)siloxane).

The carbazole functional polymer thus prepared is reacted with tetracyanoethylene under the conditions set forth in Example I. The concentration of tetracyanoethylene used in such synthesis is three times the mole equivalent of the carbazole functional groups present on this polymer.

EXAMPLE XIV - XIX

The following carbazole functional polymers can be prepared by techniques analogous to those described in Example XIII.

    ______________________________________                                         Example No. Carbazole Functional Polymer                                       ______________________________________                                         XIV         poly(methyl(N-ethyl-3-carbazyl)                                                siloxane)                                                          XV          poly(methyl-(N-ethyl-2-carbazyl)                                               siloxane)                                                          XVI         poly(methyl-(N-phenyl-3-carbazyl)                                              siloxane)                                                          XVII        poly(methyl-(N-phenyl-2-carbazyl)                                              siloxane)                                                          XVIII       poly(methyl-(N(p-dimethylamino-                                                phenyl)-3-carbazyl) siloxane)                                      XIX         poly(methyl-(N(p-dimethylamino-                                                phenyl)2-carbazyl) siloxane)                                       ______________________________________                                     

What is claimed is:
 1. A photoconductive polymer of the formula: ##SPC4##wherein X is a structural unit of the backbone of the photoconductive polymer; R is an aliphatic hydrocarbon radical having anywhere from 1 to 10 carbon atoms, phenyl or substituted phenyl, said phenyl substituent being capable of contribution of electrons to relatively electron deficient centers on the carbazyl functional group; n is the total number of carbazyl functional groups pendant from the backbone of the photoconductive polymer; and m is at lest 0.1 percent of the total number of carbazyl functional groups pendant from the backbone of the photoconductive polymer.
 2. The photoconductive polymer of claim 1 wherein at least 0.1 to about 50 percent of said carbazyl functional groups are tricyanovinylated.
 3. The photoconductive polymer of claim 1 wherein at least 0.1 to about 35 percent of said carbazyl functional groups are tricyanovinylated.
 4. The photoconductive polymer of claim 1 wherein the copolymer comprises structural units of 6-tricyanovinyl-N-ethyl-2-vinylcarbazole.
 5. The photoconductive polymer of claim 1 wherein the copolymer comprises structural units of 6-tricyanovinyl-N-ethyl-3vinylcarbazole.
 6. The photoconductive polymer of claim 1 wherein the copolymer comprises structural units from 6-tricyanovinyl-N-ethyl-2-vinylcarbazole and 6-tricyanovinyl-N-ethyl-3-vinylcarbazole 